<template>
<div class="list"> 
  <ul>
    <li class="item" v-for="item of letters" :key="item"
     @touchstart="handleTouchStart"
     @touchmove="handleTouchMove"
     @touchend="handleTouchEnd"
     @click="handleLetterClick"
     :ref="item"
    >{{item}}</li>   
  </ul>
</div>
</template>
<script>
export default {
  name: 'CityAlphabet', 
  props:{   
    allcities:Object
  },
  computed:{
     letters () {
       const letters=[]
       for(let i in this.allcities){
        letters.push(i)
       }
       return letters
     }
  },
  data() {
    return {
       touchStatus:false,
       startY:0,
       timer:null
    }   
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change2',e.target.innerText)       
    },
    handleTouchStart (){
      this.touchStatus = true
    },
    handleTouchMove (e){
      if(this.touchStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() =>{
          const touchY = e.touches[0].clientY -89
          const index = Math.floor((touchY-this.startY)/20)
          console.log(index)
          if(index >= 0 && index < this.letters.length){
             this.$emit('change2',this.letters[index])
          }
        },16)       
      }
    },
    handleTouchEnd (){
       this.touchStatus = false
    }
  }
}
</script>
<style lang="stylus" scoped>
 @import '~@/assets/styles/varibles.styl'
 .list 
  display:flex
  flex-direction:column
  justify-content:center
  position:absolute
  top:1.58rem
  right:0
  bottom:0
  width:.4rem
  .item
    text-align:center
    line-height:.44rem
    color:$bgColor
</style>
